Fabric-Based Devices With Force Sensing

ABSTRACT

A fabric-based item such as a fabric glove may include force sensing circuitry. The force sensing circuitry may include force sensor elements formed from electrodes on a compressible substrate such as an elastomeric polymer substrate. The fabric may include intertwined strands of material including conductive strands. Signals from the force sensing circuitry may be conveyed to control circuitry in the item using the conductive strands. Wireless circuitry in the fabric-based item may be used to convey force sensor information to external equipment. The compressible substrate may have opposing upper and lower surfaces. Electrodes for the force sensor elements may be formed on the upper and lower surfaces. Stiffeners may overlap the electrodes to help decouple adjacent force sensor elements from each other. Integrated circuits can be attached to respective force sensing elements using adhesive.

This patent application is a continuation of patent application Ser. No.16/206,851, filed on Nov. 30, 2018, which is a continuation of patentapplication Ser. No. 15/940,876, filed on Mar. 29, 2018, now U.S. Pat.No. 10,180,721, which claims the benefit of provisional patentapplication No. 62/519,564, filed on Jun. 14, 2017, which are herebyincorporated by reference herein in their entireties.

FIELD

This relates generally to force sensing and, more particularly, to itemssuch as fabric-based items with force sensing capabilities.

BACKGROUND

It may be desirable to form items using materials such as fabric. Forexample, wearable items may be formed from fabric. Some wearable itemsmay include sensing circuitry. Electronic equipment may use informationfrom the sensing circuitry in controlling a system or performing othertasks.

If care is not taken, fabric-based items such as these may not offerdesired features. For example, a fabric-based item with sensingcircuitry may be awkward to use, may not have an attractive appearance,or may not gather measurements accurately.

SUMMARY

A fabric-based item such as a fabric glove may include force sensingcircuitry. The force sensing circuitry may include force sensor elementsformed from electrodes on a compressible substrate such as anelastomeric polymer substrate. The fabric may include intertwinedstrands of material including conductive strands. Signals from the forcesensing circuitry may be conveyed to control circuitry in the item usingthe conductive strands. Wireless circuitry in the fabric-based item maybe used to convey force sensor information to external equipment.

The compressible substrate may have opposing upper and lower surfaces.Electrodes for the force sensor elements may be formed on the upper andlower surfaces. Stiffeners may overlap the electrodes to help decoupleadjacent force sensor elements from each other. In some configurations,integrated circuits can be attached to respective force sensing elementsusing adhesive.

Force sensing elements may have sets of electrodes that are arranged inan array on the compressible substrate such as a one-dimensional array.The compressible substrate may be formed from an elongated strip of theelastomeric polymer and may be sufficiently elongated to serve as astrand that is intertwined with the conductive strands and otherintertwined strands of material in the fabric.

To facilitate deformation of the compressible substrate, thecompressible substrate may be provided with openings surrounding theelectrodes of each force sensor element. Electrodes, signal traces forconveying capacitive force sensor signals, shield structures, and otherconductive signal paths in the force sensing circuitry may be formedfrom structures that resist cracking when flexed such as mesh structureswith serpentine line segments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an illustrative fabric-based item inaccordance with an embodiment.

FIG. 2 is a side view of illustrative woven fabric in accordance with anembodiment.

FIG. 3 is a top view of illustrative knit fabric in accordance with anembodiment.

FIG. 4 is a diagram of an illustrative fabric-based item such as a glovewith sensor circuitry coupled to an electronic device in accordance withan embodiment.

FIG. 5 is a cross-sectional side view of an illustrative glove fingerwith sensor circuitry such as force sensors in accordance with anembodiment.

FIG. 6 is a cross-sectional side view of an illustrative capacitiveforce sensor in accordance with an embodiment.

FIGS. 7 and 8 are diagrams of illustrative arrays of electrodes forcapacitive force sensors in accordance with an embodiment.

FIG. 9 is a cross-sectional side view of an illustrative capacitiveforce sensor in accordance with an embodiment.

FIG. 10 is a top view of an illustrative strip-shaped substrate andassociated array of force sensor elements incorporated into fabric inaccordance with an embodiment.

FIG. 11 is a top view of an illustrative force sensor in accordance withan embodiment.

FIG. 12 is a cross-sectional side view of the force sensor of FIG. 11 inaccordance with an embodiment.

FIG. 13 is a diagram of an illustrative conductive mesh structure of thetype that may be used in forming conductive paths in force sensorcircuitry in accordance with an embodiment.

FIG. 14 is a top view of an illustrative force sensor formed from metaltraces on an elastomeric layer having through-holes or other openings tofacilitate deformation of the elastomeric layer in accordance with anembodiment.

FIG. 15 is a top view of illustrative fabric having an array of forcesensors in accordance with an embodiment.

FIG. 16 is a cross-sectional side view of an illustrative force sensorformed from an integrated circuit that is coupled to signal lines suchas conductive strands in a fabric layer and that is attached to anelastomeric layer with capacitive electrodes that are separated by theelastomeric layer in accordance with an embodiment.

FIG. 17 is a cross-sectional side view of another illustrative forcesensor formed from an integrated circuit and capacitive electrodesseparated by an elastomeric layer that is attached to the integratedcircuit in accordance with an embodiment.

FIG. 18 is a cross-sectional side view of an illustrative force sensorbeing molded into a finger shape in accordance with an embodiment.

FIG. 19 is a cross-sectional side view of an illustrative yarn-basedforce sensor in accordance with an embodiment.

DETAILED DESCRIPTION

A schematic diagram of an illustrative item that contains force sensorsis shown in FIG. 1. Item 10 may be an electronic device or an accessoryfor an electronic device such as a laptop computer, a computer monitorcontaining an embedded computer, a tablet computer, a cellulartelephone, a media player, or other handheld or portable electronicdevice, a smaller device such as a wrist-watch device, a pendant device,a headphone or earpiece device, a device embedded in eyeglasses or otherequipment worn on a user's head, or other wearable or miniature device,a television, a computer display that does not contain an embeddedcomputer, a gaming device, a remote control, a navigation device, anembedded system such as a system in which item 10 is mounted in a kiosk,in an automobile, airplane, or other vehicle, other electronicequipment, or may be equipment that implements the functionality of twoor more of these devices. If desired, item 10 may be a removableexternal case for electronic equipment, may be a strap, may be a wristband or head band, may be a removable cover for a device, may be a caseor bag that has straps or that has other structures to receive and carryelectronic equipment and other items, may be a necklace or arm band, maybe a wallet, sleeve, pocket, or other structure into which electronicequipment or other items may be inserted, may be part of a chair, sofa,or other seating (e.g., cushions or other seating structures), may bepart of an item of clothing or other wearable item (e.g., a hat, belt,wrist band, headband, sock, glove, shirt, pants, etc.), or may be anyother suitable item. Configurations in which item 10 is a glove or otherwearable item may sometimes be described herein as an example. This is,however, merely illustrative. Item 10 may be any suitable device.

Item 10 may include intertwined strands of material that form fabric 12,so items such as item 10 may sometimes be referred to as fabric-baseditems or fabric-based electronic devices. Fabric 12 may form all or partof a housing wall or other layer in an electronic device (e.g., whenitem 10 is a glove or other flexible device worn by a user), may form anouter covering for a housing wall structure, may form internalstructures in an electronic device, or may form other fabric-basedstructures. Item 10 may be soft (e.g., item 10 may have a fabric surfacethat yields to a light touch), may have a rigid feel (e.g., the surfaceof item 10 may be formed from a stiff fabric), may be coarse, may besmooth, may have ribs or other patterned textures, and/or may be formedas part of a device that has portions formed from non-fabric structuresof plastic, metal, glass, crystalline materials, ceramics, or othermaterials.

The strands of material in fabric 12 may be single-filament strands(sometimes referred to as fibers or monofilaments), may be yarns orother strands that have been formed by intertwining multiple filaments(multiple monofilaments) of material together, or may be other types ofstrands (e.g., tubing). Monofilaments for fabric 12 may include polymermonofilaments and/or other insulating monofilaments and/or may includebare wires and/or insulated wires. Monofilaments formed from polymercores with metal coatings and monofilaments formed from three or morelayers (cores, intermediate layers, and one or more outer layers each ofwhich may be insulating and/or conductive) may also be used.

Yarns in fabric 12 may be formed from polymer, metal, glass, graphite,ceramic, natural materials as cotton or bamboo, or other organic and/orinorganic materials and combinations of these materials. Conductivecoatings such as metal coatings may be formed on non-conductivematerial. For example, plastic yarns and monofilaments in fabric 12 maybe coated with metal to make them conductive. Reflective coatings suchas metal coatings may be applied to make yarns and monofilamentsreflective. Yarns may be formed from a bundle of bare metal wires ormetal wire intertwined with insulating monofilaments (as examples).

Strands of material may be intertwined to form fabric 12 usingintertwining equipment such as weaving equipment, knitting equipment, orbraiding equipment. Intertwined strands may, for example, form wovenfabric, knit fabric, braided fabric, etc. Conductive strands andinsulating strands may be woven, knit, braided, or otherwise intertwinedto form contact pads that can be electrically coupled to conductivestructures in item 10 such as the contact pads of an electricalcomponent. The contacts of an electrical component may also be directlycoupled to an exposed metal segment along the length of a conductiveyarn or monofilament.

Conductive and insulating strands may also be woven, knit, or otherwiseintertwined to form conductive paths. The conductive paths may be usedin forming signal paths (e.g., signal buses, power lines, etc.), may beused in forming part of a capacitive touch sensor electrode, a resistivetouch sensor electrode, a force sensor electrode, or other input-outputdevice, or may be used in forming other patterned conductive structures.Conductive structures in fabric 12 may be used in carrying powersignals, digital signals, analog signals, sensor signals, controlsignals, data, input signals, output signals, or other suitableelectrical signals.

Item 10 may include mechanical structures in addition to fabric 12 suchas polymer binder to hold strands in fabric 12 together, supportstructures such as frame members, housing structures (e.g., anelectronic device housing), and other mechanical structures.

Item 10 may include circuitry 30. Circuitry 30 may include electricalcomponents that are coupled to fabric 12, electrical components that arehoused within an enclosure formed by fabric 12 and/or an enclosureformed using other housing structures such as housing walls formed fromplastic, metal, glass, ceramic, or other materials, electricalcomponents that are attached to fabric 12 using welds, solder joints,adhesive bonds (e.g., conductive adhesive bonds such as anisotropicconductive adhesive bonds or other conductive adhesive bonds), crimpedconnections, or other electrical and/or mechanical bonds. Circuitry 30may include metal structures for carrying current, electrical componentssuch as integrated circuits, discrete components (e.g., capacitors,resistors, and inductors), and/or other circuitry.

As shown in FIG. 1, circuitry 30 may include input-output circuitry 26and control circuitry 16. Input-output circuitry 26 may include forcesensors 14 (sometimes referred to as pressure sensors) and other sensorsand input-output devices 18. Devices 18 may include light-emittingdiodes, displays, speakers, microphones, buttons, tone generators,haptic output devices such as vibrators, and sensors (e.g., gas sensors,gas pressure sensors, temperature sensors, strain gauges,accelerometers, proximity sensors, touch sensors, ambient light sensors,digital image sensors, fingerprint sensors, gaze detection and eye andface sensing devices, and/or other sensors).

Control circuitry 16 may be formed from one or more integrated circuitssuch as microprocessors, microcontrollers, application-specificintegrated circuits, digital signal processors, and/or other circuits.Control circuitry 16 may be used to gather information from user inputcircuitry, sensing circuitry such as touch sensors, proximity sensors,and other sensing circuitry, and other input-output devices 18 and maybe used in gathering and processing force sensor information from forcesensors 14. Control circuitry 16 may be used to control the operation ofitem 10 based on this gathered information and/or based on otherinformation by controlling electrically controllable (electricallyadjustable) components in circuitry 16. The control circuitry may havewireless communications circuitry and other communications circuitry andmay be used in supporting communications with external equipment. Usingwireless communications or wired communications, control circuitry initem 10 may, if desired, provide information such as force sensorinformation and/or other information gathered using input-output devices18 to external equipment.

External equipment that communicates with item 10 may include separateitems that are configured to operate with each other. For example, item10 may be a case that operates with a device that fits within the case.As another example, item 10 may be a force sensing glove or otherwearable device and may be used in controlling an electronic device thatis using information such as force sensor measurements from forcesensors in item 10. Devices that may be controlled using force sensorinformation from a force sensing glove or other item 10 include a gamingunit, a computer, a set-top box, a television, and or other electronicequipment.

To supply force sensor measurements (e.g., raw measurements or commandsor other information derived from raw measurements) to externalequipment, circuitry 16 may include wireless communications circuitrysuch as antennas, wireless radio-frequency transceivers (e.g.,transceivers operating at 2.4 GHz, 5 GHz, and/or other wirelesscommunications frequencies) and other electrical components forsupporting wireless communications with external electronic devices. Ifdesired, the wireless communications circuitry may be based on infraredtransmitters such as infrared light-emitting diodes or lasers fortransmitting infrared commands to electronic equipment.

Fabric 12 may be used in forming a force sensing glove or otherelectronic device. The fabric may serve as a supporting structure forthe body of the glove or other device or, in some configurations, mayserve as an inner liner, outer covering, or other portion of asupporting structure that also includes other structural components.Fabric 12 may be formed from strands that are intertwined using anysuitable intertwining equipment. With one suitable arrangement, whichmay sometimes be described herein as an example, fabric 12 may be wovenfabric formed using a weaving machine. In this type of illustrativeconfiguration, fabric 12 may have a plain weave, a basket weave, a satinweave, a twill weave, or variations of these weaves, may be athree-dimensional woven fabric, or may be other suitable fabric. Withother suitable arrangements, fabric 12 may be knit or braided. Ifdesired, signal paths formed from conductive yarns and monofilaments(e.g., insulated and bare wires) may be used to route signals withinitem 10 and may be used to route signals between item 10 and externaldevices.

A cross-sectional side view of illustrative woven fabric 12 is shown inFIG. 2. As shown in FIG. 2, fabric 12 may include strands 20 such aswarp strands 20A and weft strands 20B. In the illustrative configurationof FIG. 2, fabric 12 has a single layer of woven strands 20. Multi-layerfabric constructions may be used for fabric 12 if desired.

As shown in FIG. 3, fabric 12 may be a knit fabric. In the illustrativeconfiguration of FIG. 3, fabric 12 has a single layer of knit strands 20that form horizontally extending rows of interlocking loops (courses 22)and vertically extending wales 24. Other types of knit fabric may beused in item 10, if desired.

Item 10 may include non-fabric materials (e.g., structures that areformed from plastic, metal, glass, ceramic, crystalline materials suchas sapphire, leather, etc.). These materials may be formed using moldingoperations, extrusion, machining, laser processing, and otherfabrication techniques and may be used in forming housing structures,internal mounting structures, buttons, portions of display componentsand other electronic components, and/or other structures in item 10. Insome configurations, item 10 may include one or more layers of material.The layers in item 10 may include layers of polymer, metal, glass,fabric, leather, adhesive, crystalline materials, ceramic, substrates onwhich components have been mounted, patterned layers of material, layersof material containing patterned metal traces, thin-film devices such astransistors, and/or other layers.

As shown in FIG. 4, item 10 may include a layer of fabric 12 and/orother layers of material shaped in the form of a glove. Force sensingcircuitry such as force sensors 14 may be located on one or more fingers38 of the glove (e.g., on the top, bottom, and/or sides of fingers 38)and/or on other areas of the glove such as on palm 40 or the top surfaceof the glove that covers the back of a user's hand. Signal paths 32 maybe used in electrically coupling force sensors 14 to control circuitry16. Signal paths 32 may be formed from conductive strands 20 in fabric12 and/or separate conductive strands (wires, traces on printedcircuits, etc.). Control circuitry 16 may have wired or wirelesscommunications circuitry for supporting communications overcommunications link 36 between item 10 and external electronic devicessuch as electronic device 34. Device 34 may be a computer, cellulartelephone, a head-mounted device, a display, a gaming unit, a set-topbox, a system including two or more of these devices, or otherelectronic equipment. During operation, control circuitry 16 may useforce sensors 14 to gather force sensor measurements and may, as anexample, provide this information to electronic device 34 forcontrolling device 34. If desired, control circuitry in externalequipment 34 may be used in processing sensor data (e.g., to minimizethe amount of circuitry in item 10). Force sensor measurements may beused in a glove or other input device, in clothes, as part of a heartrate sensor, blood pressure sensor, respiration sensor, etc.

FIG. 5 is a cross-sectional side view of an illustrative portion of item10 (e.g., a glove) such as a finger portion. As shown in FIG. 5, glovefinger 38 may include fabric 12 that has been woven, knit, braidedand/or sewn to form a shape appropriate for receiving a user's finger(e.g., finger 42). When the user presses glove finger 38 in direction 46towards surface 44 with finger 42, a compressive force will be appliedto fabric 12 and force sensors 14 between finger 42 and surface 44.Surface 44 may be an external surface such as a table top or may be aninner surface of a glove-shaped outer shell (housing) against which theuser may press. Control circuitry 16 (FIG. 4) can measure this forceusing force sensors 14.

An illustrative force sensor is shown in FIG. 6. Force sensor 14 mayinclude capacitive force sensor processing circuitry such as circuitry48 and a capacitive force sensor element such as force sensor element50. Capacitive force sensor circuitry 48 may be implemented using one ormore integrated circuits and may be used to apply alternating currentsignals to elements such as element 50 (e.g., drive signals D) whilemonitoring resulting signals (sense signals S). By processing the D andS signals, circuitry 48 can measure the capacitance of element 50 andcan detect any changes to this capacitance due to applied force. Anysuitable capacitance sensing techniques may be used in processingcapacitance measurements (e.g., mutual capacitance or self capacitance).

Element 50 may include capacitive force sensing electrodes 52 and 54.Conductive strands in fabric 12 and/or other signal paths may be used inelectrically coupling capacitive force sensor circuitry 48 to electrodes52 and 54. Electrodes 52 and 54 may be separated by substrate 56.Substrate 56 may be formed from an elastomeric polymer such as siliconeor other compressible material. Elastomeric polymer substrate 56 may beinsulating. When no force is applied to element 50, electrodes 52 and 54will be separated by a distance Dl. When force is applied to element 50in directions 58 and 59, elastomeric polymer substrate 56 will deforminwardly and the distance between electrodes 52 and 54 will decrease todistance D2. This will cause the capacitance between electrodes 52 and54 to rise, which can be detected by capacitive force sensor circuitry48.

There may be any suitable number of elements 50 and any suitable numberof integrated circuits for implementing circuitry 48 in item 10. FIG. 7is a diagram of an illustrative force sensor formed from multiplevertical strip-shaped electrodes 52 that carry drive signal D andmultiple horizontal strip-shaped electrodes 54 that provide sensesignals S to circuitry 48. Electrodes 52 and 54 may run perpendicular toeach other and may be formed form metal traces on opposing sides of anelastomeric layer such as elastomeric polymer substrate 56 of FIG. 6.The electrode pattern of FIG. 7 allows two-dimensional forcemeasurements (in dimensions X and Y) to be gathered by circuitry 16. Inthe illustrative configuration of FIG. 8, drive electrodes 52 receive acommon drive signal D and each sense electrode 54 is coupled to anindependent sense signal line for providing a respective independentsense signal to circuitry 48. In configurations such as these, eachintersection between drive and sense electrodes serves as a separateelement 50. Electrodes 52 and 54 of FIGS. 7 and 8 may be separated by acompressible material such as an elastomeric material (e.g., substrate56). If desired, other electrode patterns may be used in forming forcesensor 14. The configurations of FIGS. 7 and 8 are merely illustrative.

FIG. 9 is a cross-sectional side view of an illustrative capacitiveforce sensor element. As shown in FIG. 9, element 50 may have acompressible layer such as elastomeric polymer substrate 56 thatseparates electrodes 52 and 54 as described in connection with FIG. 6.When polymer substrate 56 is compressed, the separation distance T1between electrodes 52 and 54 decreases to a distance D2 that is lessthan distance T1 as illustrated by compressed electrode positions 52′and 54′. This changes the capacitance between electrodes 52 and 54,which can be measured and used in determining how much force has beenapplied to element 50.

Optional stiffeners 60 may be formed on top of electrodes 52 and 54 tohelp decouple sensor element 50 from adjacent sensor elements 50 (e.g.,to help reduce cross-talk). If desired, there may be multiple stiffenerstructures over each pair of electrodes (e.g., stiffener 60 of FIG. 9may be segmented by forming gaps 61 that divide stiffeners 60 to formsmaller stiffener segments). In some arrangements, only one stiffener 60is used (e.g., lower stiffener structures may be omitted from electrode52 so that only the stiffener structure on electrode 54 is present).

The thickness T1 of the layer of elastomeric polymer substrate 56 inelement 50 may be, for example, 20-100 microns, at least 3 microns, atleast 15 microns, at least 40 microns, less than 400 microns, less than200 microns, or other suitable thickness. The thickness T2 of stiffeners60 may be, for example, 50-300 microns, at least 10 microns, at least 25microns, less than 1000 microns, less than 500 microns, or othersuitable thickness. Stiffeners 60 may be formed form a polymer, metal,or other material that is more rigid than elastomeric polymer substrate56. For example, elastomeric polymer substrate 56 may be formed from anelastomeric polymer characterized by a first modulus of elasticity(e.g., a Young's modulus or other elastic modulus) and stiffeners 60 maybe characterized by a second modulus of elasticity that is greater thanthe first modulus of elasticity. The Young's modulus of elasticity ofpolymer substrate 56 may be 0.1 MPa to 10 MPa, greater than 0.2 MPa,less than 5 MPa, etc. The Young's modulus of elasticity of stiffeners 60may be 100 MPa to 200 GPa, more than 150 MPa, less than 150 GPa, etc.The thickness of electrodes 52 and 54 may be less than 20 microns, lessthan 10 microns, less than 3 microns, less than 0.5 microns, more than0.01 microns, more than 0.2 microns, or other suitable thickness.Electrodes 52 and 54 may be formed from metal traces (e.g., metal tracesdeposited using physical vapor deposition, electroplating, etc.) and/ormay be formed form patterned conductive structures such as patternedmetal ink (e.g., printed silver paint or other metal paint, graphene,graphite, silver particles, or other conductive material in a polymersuch as silicone, PEDOT:PSS or poly(3,4-ethylenedioxythiophene)polystyrene sulfonate conductive polymer, etc.). The width WD ofstiffeners 60 and electrodes 54 and 52 (e.g., the diameter or otherlateral dimension in the XY plane of FIG. 9) may be 2-3 mm, at least 0.1mm, at least 0.5 mm, at least 1 mm, less than 10 mm, less than 4 mm, orother suitable dimension. Stiffeners 60 help translate applied pressureon the surface of stiffeners 60 into compression of the elastomericmaterial directly between the stiffeners, thereby helping to avoidundesired coupling between adjacent elements 50 that could reducemeasurement accuracy. The use of locally stiff areas (e.g., stiffeners60) and the use of a flexible substrate that allows individual sensorsto be compressed without crosstalk helps to accommodate variations infabric morphology and finger curvature while minimizing longitudinalsubstrate stress.

To facilitate incorporation of force sensor 14 into fabric 12, sensorelements 50 may be formed on an elongated strip-shaped flexiblesubstrate such as elastomeric polymer substrate 56 of FIG. 10. Theaspect ratio of substrate 56 (length over width) may be at least 10, atleast 25, at least 100, less than 1000, or other suitable aspect ratio.Sensor elements 50 may, in general, be arranged in a two-dimensionalarray (e.g., extending across both the X and Y dimensions when sensor 14lies in an XY plane) or a one-dimensional array. Sensor 14 of FIG. 10has a one-dimensional array configuration in which substrate 56 iselongated along the Y axis and in which sensor elements 50 are arrangedin a single row extending along the Y axis. If desired, narrowstrip-shaped sensors can be formed using multiple closely spaced rows ofelements 56 (e.g., a 2×N arrangement in which N is the number ofelements 50 that extend along the longitudinal axis of the sensorsubstrate). The use of a narrow sensor substrate arrangement with asingle one-dimensional array of elements 50 and/or a relatively narrowtwo-dimensional array of elements 50 allows sensor 14 to form a strandof material that can be incorporated into fabric 12 amongst otherstrands 20 as shown in FIG. 10. Strands formed from elongatedcompressible substrates and narrow arrays of force sensor elements 50may serve as warp strands or weft strands in woven fabric or may beincorporated into knit or braided fabric.

If desired, electrical shielding structures may be incorporated intosensors 14. For example, grounded conductive layers may be formed aboveand/or below sensor signal paths. This type of arrangement is shown inthe top view of sensor element 50 in FIG. 11 and the corresponding sideview of FIG. 12. As shown in FIGS. 11 and 12, sensor element 50 mayinclude electrodes 54 and 52 that are located on opposing surfaces of ansubstrate 56 Grounded shielding structures such as shield layer G2 andshield layer G1 may help shield signal paths in element 50. For example,shield G1 may be formed on the upper surface of substrate 56 and shieldG2 may be formed on the opposing lower surface of substrate 56 so thatthese shield layers overlap portions of electrodes 52 and 54. Substrate56 may be formed from multiple elastomeric layers such as layer 56A and56B. Layers 56A and 56B may be coupled together (e.g., using a layer ofadhesive). Electrode 52 may be formed between layers 56A and 56B (as anexample). Optional stiffeners 60 may be formed on both electrode 54 andthe opposing side of substrate 56 (e.g., on shield G2 where shield G2overlaps electrode 54) and/or one or both of these stiffeners may beomitted. If desired, shields can be formed around drive electrode 54. Insome configurations, conductive strands in fabric can form shields.

To prevent cracks from forming in the conductive layers of sensor 14,one or more of these conductive layers may be formed using serpentinelines. As an example, one or more conductors in sensor 14 such aselectrodes 52 and 54 and shielding layers G1 and G2 may be formed usinga mesh of serpentine lines (see, e.g., serpentine lines 72 of mesh 70 inthe example of FIG. 13). Isolated (non-mesh-shaped) paths formed fromserpentine lines may also be used (e.g., to convey signals between forcesensor elements 50 and force sensor processing circuitry). Lines 72 maybe formed from metal traces deposited and patterned on substrate 56using photolithography and/or may be metal layers formed from metalpaint or other conductive materials.

To enhance the flexibility of substrate 56, one or more areas ofsubstrate 56 may be provided with openings. The openings may be recessesthat pass partially through substrate 56 and/or may be through holesthat pass between opposing surfaces of substrate 56.Flexibility-enhancement structures such as these may, if desired, beconcentrated around electrodes 52 and 54 to facilitate compression ofthe portion of substrate 56 that overlaps electrodes 52 and 54. As shownin FIG. 14, for example, openings 74 that pass partly or entirelythrough substrate 56 may be arranged in a ring-shaped pattern such as acircular ring surrounding electrodes 52 and 54. This may facilitatecompression of the portion of substrate 56 that is interposed betweenelectrodes 52 and 54 when a user compresses force sensing element 50during use of item 10.

In the arrangement of FIG. 15, fabric 12 includes woven strands such aswarp strands 20A and weft strands 20B. Force sensing elements 50 may beformed at intersections 76 of strands 20A and 20B (e.g., at theintersections of conductive strands among strands 20A and 20B) and maybe electrically coupled to these strands. This allows signals for theforce sensor elements to be routed through the conductive strands offabric 12. Signals can also be routed through signal paths (wires,flexible printed circuits, etc.) that are separate from fabric 12, ifdesired.

FIG. 16 is a cross-sectional side view of an illustrative force sensorthat includes an integrated circuit. As shown in FIG. 16, electrodes 52and 54 of force sensing element 50 may be formed on opposing sides ofsubstrate 56. Integrated circuit 80 may have terminals such as contacts82 and 86. Contact 82 may be shorted to electrode 54. Via 78 may beformed from a conductor such as metal to short electrode 52 to contact86. If desired, adhesive 88 (e.g., a polymer layer) may be used toattach integrated circuit 80 to substrate 56. Integrated circuit 80 maybe a bare integrated circuit die (e.g., a silicon die) or may be apackaged integrated circuit (e.g., an integrated circuit die or diesmounted in package formed of plastic, ceramic, and/or other materials).

Integrated circuit 80 may include capacitive force sensor circuitry 48of FIG. 6 and may analyze capacitive electrode measurements made usingelectrodes 54 and 52 to produce force sensor readings for use by controlcircuitry 16. Optional stiffener structures such a structure 60 may beplaced on electrode 52. Integrated circuit 80 may serve as a stiffenerfor electrode 54. Integrated circuit 80 may be coupled to controlcircuits in item 10 (e.g., control circuitry 16 of FIG. 4) usingconductive paths such as conductive strands in fabric 12 or otherconductive paths in item 10. Conductive strands of fabric 12 may beelectrically coupled to integrated circuit terminals such as contacts 90and 92 using solder, conductive adhesive, or other conductive material.

The signal paths in fabric 12 or other signal paths in item 10 thatcouple each integrated circuit 80 to control circuitry 16 may be used inconveying force measurements from force sensor elements 50 to controlcircuitry 16. One or more force sensor elements 50 may be coupled toeach integrated circuit 80 to form force sensor circuitry for item 10.For example, there may be only a single element 50 coupled to eachintegrated circuit 80 or multiple elements 50 may be coupled to a givenintegrated circuit 80. Fabric 12 may be formed above and/or below forcesensor components such as integrated circuit 80 and force sensorelement(s) 50. For example, force sensor 14 may be embedded withinfabric 12.

In the illustrative configuration of FIG. 17, electrodes 52 and 54 havebeen placed on integrated circuit 80. Force sensor electrode 94 may becapacitively coupled to electrode 52 through substrate 56 and may becapacitively coupled to electrode 54 through substrate 56. Optionalstiffener 60 may be formed on electrode 94. When the substrate materialbetween electrode 94 and electrodes 52 and 54 is compressed by anapplied force, the capacitive force sensor circuitry in integratedcircuit 80 can detect the resulting capacitance change between electrode52 and 54 to measure the applied force.

FIG. 18 shows how sensor 50 may be molded into the shape of a finger.After forming sensor elements 50 on substrate 56, heat and pressure maybe applied to substrate 56 using finger-shaped molds 150. After molds150 are removed, substrate 56 retains its molded shape, therebyproducing force sensor circuitry in which substrate 56 and the array ofelements on substrate 56 have compound curvature configured to receive afinger of a user. If desired, circuitry such as sensor elements 50 maybe formed after substrate 56 has been molded into its desired shape(e.g., a finger shape having surfaces with compound curvature).

FIG. 19 shows how force sensor circuitry may be integrated into a yarn.Shield SH, sense line S, and drive line D may be formed from conductivestrands of material. Portions of sense line S and drive line D and/orconductive traces on elastomeric substrate 56 (covered with optionalstiffeners 60) may be used in forming electrodes for force sensingelement 50. Shield SH may be braided with sense line S and drive line D.With one illustrative configuration, shield line SH may be twistedaround sense line S to shield sense line S from interference with driveline D and drive line D may be loosely wrapped around both sense line Sand shield line SH. In this way, a braided yarn with integral forcesensing elements 50 along its length may be formed.

The foregoing is merely illustrative and various modifications can bemade to the described embodiments. The foregoing embodiments may beimplemented individually or in any combination.

What is claimed is:
 1. A wearable electronic device comprising: fabriccontaining conductive strands of material; control circuitry coupled tothe conductive strands of material; a force sensor element coupled tothe control circuitry; and force sensor circuitry that is electricallycoupled to the force sensor element through the conductive strands ofmaterial.
 2. The wearable electronic device defined in claim 1 whereinthe conductive strands form at least part of the force sensor.
 3. Thewearable electronic device defined in claim 2 wherein a portion of theforce sensor is embedded in the fabric.
 4. The wearable electronicdevice defined in claim 3 wherein the force sensor circuitry comprisescapacitive force sensor circuitry.
 5. The wearable electronic devicedefined in claim 4 wherein the force sensor element includes acompressible substrate and first and second electrodes that arerespectively located on first and second opposing surfaces of thecompressible substrate.
 6. The wearable electronic device defined inclaim 5 wherein the force sensor comprises a metal shielding layer onthe compressible substrate.
 7. The wearable electronic device defined inclaim 6 wherein the force sensor element comprises a metal layer on thecompressible substrate having serpentine signal paths.
 8. The wearableelectronic device defined in claim 1 wherein the fabric is configured tobe worn on a user's finger.
 9. The wearable electronic device defined inclaim 1 wherein the force sensor includes vertical strip-shapedelectrodes and horizontal strip-shaped electrodes that overlap thevertical strip-shaped electrodes.
 10. The wearable electronic devicedefined in claim 9 wherein the force sensor is configured to maketwo-dimensional force measurements using the vertical strip-shapedelectrodes and the horizontal strip-shaped electrodes.
 11. A wearableelectronic device, comprising: a fabric; control circuitry; and a forcesensor coupled to the control circuitry and to the fabric, wherein theforce sensor includes first electrodes that extend in a first dimensionand second electrodes that extend in a second dimension that isdifferent from the first dimension, wherein the second electrodesoverlap the first electrodes.
 12. The wearable electronic device definedin claim 11 wherein the second electrodes are separated from the firstelectrodes by a compressible material.
 13. The wearable electronicdevice defined in claim 12 wherein the compressible material forms firstand second elastomeric layers, wherein the second electrode is betweenthe first and second elastomeric layers and wherein the first electrodeis on the first elastomeric layer and separated from the horizontalstrip-shaped electrode by the first elastomeric layer.
 14. The wearableelectronic device defined in claim 13 wherein the first and secondelastomeric layers are configured to compress in response to forceapplied to the force sensor, thereby changing a capacitance between thefirst and second electrodes.
 15. The wearable electronic device definedin claim 11 wherein the force sensor further comprises an electricalshield and conductive traces that couple the first and second electrodesto capacitive force sensor circuitry.
 16. An apparatus configured to beworn on a user's finger, comprising: fabric formed from intertwinedstrands of material; control circuitry; and a force sensor coupled tothe fabric and electrically coupled to the control circuitry.
 17. Theapparatus defined in claim 16 wherein the force sensor is embedded inand integral with the fabric.
 18. The apparatus defined in claim 16wherein the intertwined strands of material include conductive strandsand wherein at least a portion of the force sensor is formed from theconductive strands.
 19. The apparatus defined in claim 16 wherein theforce sensor comprises first and second electrodes separated by acompressive material, wherein the compressive material is configured tocompress in response to a force from the user's finger.
 20. Theapparatus defined in claim 16 wherein the fabric forms a glove that isconfigured to be worn on the user's hand.